1. Field of the Invention
The present invention relates to a ranging method of a mobile station in a legacy support mode. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for a mobile station to perform a ranging in a mobile communication system having a legacy system and an advanced system coexist therein using a legacy support frame.
2. Background Art
Generally, a base station in a system capable of supporting both a legacy mobile station and an advanced system mobile station operates in a mixed mode. In the following description, such a mixed mode operation is explained on the assumption that a legacy system is IEEE 802.16e system and that an advanced system is IEEE 802.16m system.
A mixed mode is divided into a WirelessMAN OFDMA region (hereinafter named an L region) supporting a legacy mobile station (i.e., IEEE 802.16e mobile station) and an advanced wireless interface region (hereinafter named an M region) supporting IEEE 802.16m mobile station. In the mixed mode, an uplink (UL) region is operable in a manner that the L and M regions are divided by TDM (time division multiplexing) or FDM (frequency division multiplexing). A ranging channel of the conventional IEEE 802.16e system uses a PUSC structure in diversity mode. On the contrary, a ranging channel of the IEEE 802.16m system uses a subband CRU (contiguous resource unit) structure.
FIG. 1 is a diagram of a TDD frame structure for supporting WielessMAN-OFDMA uplink FDM operation.
Referring to FIG. 1, a frame structure includes a WirelessMAN OFDMA downlink region and an advanced wireless interface downlink region. And, in downlink, the WirelessMAN OFDMA downlink region and the advanced wireless interface downlink region are divided by TDM. Moreover, in uplink, the L region and the M region are divided by FDM. In particular, in time domain, the WirelessMAN OFDMA downlink region, the advanced wireless interface downlink region and an FDM multiplexed uplink region correspond to a WirelessMAN frame having a 5 ms length. In case of the advanced wireless interface frame, the WirelessMAN OFDM downlink region is regarded as a frame offset and a length of 5 ms from the frame offset is regarded as a frame.
Since a system configured to operate by FDM is structurally unable to use different permutations, the IEEE 802.16m mobile station should use a ranging channel structure of the IEEE 802.16e system as it is. In particular, the corresponding system can be designed in a following manner. First of all, a ranging channel is allocated to an L region only in consideration of an overhead. And, the corresponding ranging channel is designed to use by being shared with IEEE 802.16m mobile stations. Alternatively, it is able to design the ranging channel to be allocated to an M region as well as the L region.